Indicator compositions and devices are used in many industries such as the medical, dental, veterinary, and food industries to provide evidence regarding the history of a product's exposure to various environmental conditions. Although electronic devices are available to monitor environmental conditions, such as temperature, humidity, pressure, UV exposure, pollutants, and others like these, such devices are typically too expensive to incorporate into individual packages. Thus, simpler indicator compositions and devices using inexpensive chemistry provide a more economical way to monitor exposure to environmental conditions.
In some uses, an indicator composition is designed to provide a warning that a product has been exposed to unwanted environmental conditions. For example, meat and dairy products can include a sensor derived from an indicator composition designed to reveal unsafe exposures to certain temperatures over a period of time. These indicator compositions are sometimes known as “time-temperature indicators” or TTI's. Such TTI's can be used for monitoring time and temperature exposures of a wide variety of items including food and medical products. Unlike expiration dates on products, which are merely recommendation dates based on expected transport and storage conditions that are unknown to the consumer, TTI's can be designed to respond directly to the temperature to which the product is exposed and then reflect the actual temperature history of the product. Commercial distributors of food and pharmaceuticals commonly attach or print TTI's onto shipping boxes. The most common purpose is to ensure the integrity of the supply chain from manufacturer to the customer.
A TTI can be matched to a particular perishable product or to particular use. Examples of perishable products for which the use of such device can be useful include but are not limited to, packaged fresh and frozen foods, dairy products, meat, pharmaceuticals, photographic film, canned goods, spices, vitamins, seeds, and plants. Other products that slowly degrade over time, and for which TTI's are useful, include paints, coatings, adhesives, caulks, and other sealants.
Temperature indicators are basically grouped into two families. A first group can signal a change only after a certain critical temperature has been reached or exceeded (threshold). A second group (such as in a TTI) can be designed to integrate over the entire temperature range and then signal a condition at any stage.
In one instance, the indicator composition is designed to provide affirmation that a desired environmental conditioning has been achieved, for example as sterilization or as cooking indicators. In hospitals, clinics, and other medical facilities, it is standard practice to sterilize various articles such as gowns, drapes, sheets, dressings, and other articles, prior to use by placing them in an autoclave where they are subjected to steam sterilization. It is common practice in sterilizing such articles to gather several articles together, bundling them in a porous wrap as a package, and placing them in an autoclave together with a sterilizing indicator article or device. This indicator device can be either inserted into or applied to the package of articles. Where pressure-sensitive adhesive tapes are used to bundle the articles, it is convenient to arrange the indicator composition on the back of the adhesive tape.
The Association for the Advancement of Medical Instrumentation {AAMI} has recommended practices and standards that cover sterilization testing, including the use of chemical indicator compositions. AAMI categorizes chemical indicator compositions in six classes as described in Sterilization of Health Care Products—Chemical Indicators—Part 1: General Requirements, American National Standards Institute (ANSI)/AAMI ST 60—41996). Class 1 relates to process indicators that are intended for use with individual packs to demonstrate that the pack has been exposed to the sterilization process and to distinguish between processed and unprocessed packs. Class 2 describes indicators for use in a specific test procedure such as a Bowie-Dick test. Class 3 relates to single parameter indicators to indicate exposure to a sterilization process at a stated value (SV) of the chosen parameter, and Class 4 relates to multi-parameter indicators that are designed to respond to two or more critical parameters and is intended to indicate exposure to a sterilization cycle at SV's of the chosen parameters (for example, time, temperature and saturated steam as critical conditions for a steam cycle). Class 5 chemical indicators are known as integrating indicators that are designed to react in response to all critical parameters over a specific range of sterilization cycles and whose performance has been correlated to the performance of the relevant biological indicator under the labeled conditions of use. Class 6 chemical indicators are emulating indicators that are intended for cycle verification and are designed to react to all critical parameters for specified sterilization cycles. They are considered to be indicative of a complete cycle by showing the presence or absence of specific time and temperature parameters during a cycle.
Surgical instruments used in medical, dental and veterinary applications are reused after sterilization in appropriate pouches. The surgical instruments can be sterilized inside a pouch using a variety of sterilizing agents such as ethylene oxide and steam. A sterilization indicator composition can be provided inside or on the pouch, for example using a printing operation, to provide a sterilization history. For example, it is common practice to sterilize surgical instruments by sealing them in vapor-permeable plastic and exposing the packaged surgical instruments to hot steam for a certain period of time. To be sure that the surgical instruments have had the appropriate exposure to steam and temperature for the requisite time, color-changing indicator compositions in the form of patches can be provided inside of the package with the surgical instruments. Typically, steam-based sterilization indicators include two active components that react with each other (at high temperature steam) to provide a color change. In some cases, however, the color-changing indicators compositions indicate a color change prematurely, giving a false indication of sterilization. To control or adjust the reactivity of the color-changing indicator compositions, one can consider altering the chemical reactants to be more stable, but this can be difficult and bring more unpredictability to the situation.
A number of efforts have been made to solve the problem noted above where “false positives” are obtained with known sterilization indicator compositions. For example, it has been desired to find an inexpensive and effective way to keep reactants separated before their reaction is needed in response to a specific environmental conditions or stimulus.
U.S. Pat. No. 8,110,628 (Nair et al.) describes the incorporation of different reactants in different pores of polymeric particles, but there is no enabling teaching as to how such distinctly isolated reactants can be used in indicator compositions.
U.S. Pat. No. 7,585,521 (Barbe et al.) describes the preparation of controlled release ceramic particles, but it fails to describe how active materials within the ceramic particles can be used in indicator compositions.
U.S. Patent Application Publication 2009/0220378 (McDonnell et al.) discloses an indicator device for determining the efficacy of an antimicrobial treatment process. The indicator device includes an active agent incorporated within an electrospun polymeric nanofiber. Copper sulfate is mentioned as a possible incorporated reactant. Nanofiber devices can be used in limited procedures.
U.S. Pat. No. 5,340,537 (Barrett) discloses temperature indicating compositions that include an aqueous binder, a color changing electron donating compound having a high melting point, and a polymeric electron accepting resin reactive with the electron donating compound.
U.S. Pat. No. 7,294,379 (Ko et al.) describes a time indicating label comprising (a) a label substrate having first and second surfaces, (b) an acid-base indicator composition, and (c) an activator composition, wherein one of (b) or (c) is on the first surface of the substrate. When (b) and (c) are brought into contact, they remain adhered and can be detected. The activator can be, for example, an organic sulfonic acid.
U.S. Pat. No. 8,183,045 (Faran) discloses a device allegedly capable of exhibiting a time-temperature dependence that comprises an upper layer carrying a first reactant selected from a group of materials such as chelating agents and a base layer carrying a second reactant adapted to react with the first reactant upon triggering. The device provides two reactants in different layers with a polymeric barrier layer between them and one of the reactants can diffuse through the barrier to react with the other.
WO2011/020185 (AR Medicom Inc.) discloses a sterilization pouch for surgical instruments that comprises a sterilant permeable sheet with a first sealing strip and a sterilant impermeable sheet with a second sealing strip. The sealing strips are sealed together to define the pouch. An indicator composition for indicating sterile processing conditions inside the pouch is located on an inner surface of the sterilant impermeable sheet.
While chemical indicator chemicals are known, it is difficult for a single material to have the precise reactivity properties needed to accurately monitor environmental conditions when the packaging used for sterilization varies from product to product. For some uses, an indicator composition is needed outside the packaging while for other uses it is needed inside the packaging. The packaging can be designed with paper or polymers, which materials have differing chemical permeabilities and thermal conductivities. Thus, when there is a need to alter or adapt the reactivity of the indicator composition to different packaging arrangements, the indicator compositions are generally prepared using different sets of chemicals. A simple system is needed wherein the reactivity of an indicator composition can be easily adapted for various applications in various packages without using a large number of alternative chemical components.
In many sterilization processes, such as sterilization of surgical instruments, indicator compositions for steam sterilization are designed to provide a visual color change after contact with saturated steam at high temperature for a specified period of time sufficient bacterial kill for Class 4 and 5 indicators. A disadvantage with known steam sterilization indicator compositions is the indicator inks contained therein can change color prematurely.
There is a need for indicator compositions that are not triggered prematurely and that can be used to accurately determine when chosen environmental conditions or multiple parameters are met. It is also desired that indicator compositions and devices are provided with simple indicator chemistry for a variety of packaging arrangements.